Smoke billows from smokestacks and a coal-fired generator at a steel factory in November 2015 in the industrial province of Hebei, China. (Kevin Frayer/Getty Images)

This story has been updated.

For the second year in a row, atmospheric carbon dioxide concentrations have climbed at a record pace. According to data from the National Oceanic and Atmospheric Administration, carbon dioxide levels jumped by three parts per million in both 2015 and 2016 and now rest at about 405 parts per million.

It’s the biggest jump ever observed at the agency’s Mauna Loa Baseline Atmospheric Observatory in Hawaii, where the measurements were recorded. Similar observations have been recorded at stations all over the world, said Pieter Tans, who leads the Carbon Cycle Greenhouse Gases group at NOAA’s Greenhouse Gas Reference Network.

Throughout the last decade, the average rate of increase has been around 2.3 parts per million per year, Tans added.

In March 2015, NOAA scientists found that the monthly global average concentration of carbon dioxide exceeded 400 parts per million for the first time. This concentration is a symbolic threshold set by scientists as a kind of milestone to help illustrate the remarkable human-caused growth of greenhouse gases in the atmosphere. For comparison, atmospheric carbon dioxide levels averaged about 280 parts per million up until the industrial revolution.

Since then, all signs have suggested that we’re now living in a permanently post-400 parts per million world. In September 2016, the time of year when atmospheric carbon dioxide levels are usually at their lowest, scientists observed that the monthly average concentration still remained above this threshold. And now, the new NOAA measurements further indicate that carbon dioxide levels are only continuing to grow — and they’re rising at breakneck speed.

It may be a little confusing to consider this news alongside other recent reports, which suggest that global carbon emissions caused by human activity have actually remained fairly flat for the past three years. The fact is, even if emissions have remained pretty stable in recent years, humans are still pouring billions of tons of greenhouse gases into the air each year.

And even if these emission levels really are starting to plateau — and it will be years before we can say whether that’s actually the case, or whether the recent flattening is just a blip on an otherwise upward trend — they’re still evening out at an all-time high, after decades of climbing. Additionally, carbon dioxide remains in the atmosphere for a long time, Tans noted. This means that new carbon dioxide emissions have a cumulative effect, adding to emissions that were already there.

“So record-high CO2 emissions, even though they stay flat, translates directly into a record-high CO2 increase” in the atmosphere, he said.

Because carbon dioxide hangs around for so long, we’ll be feeling the warming effects of this year’s jump in concentration years in the future — even if we stopped all our greenhouse gas emissions today. And Tans added that it’s not only atmospheric levels of carbon dioxide that we have to worry about, but also oceanic levels as well.

There’s a continuous gas exchange that takes place between atmosphere and ocean, Tans noted. Scientists say that at least half of all the carbon dioxide we’ve poured into the air since the industrial revolution has likely been absorbed into the sea. But it hasn’t disappeared forever, he cautioned.

“If we then proceeded by technical means — by some invention or some chemical engineering development — to pull CO2 out of the atmosphere and bury it, then the additional CO2 that’s in the oceans will come back into the atmosphere,” Tans said. Such technology, often referred to as “negative emissions,” has actually been proposed by scientists as a possible future means of combating climate change. It’s a long way from becoming a reality at the moment, but Tans noted that even if it reached that point, it still wouldn’t be able to completely reverse the climate crisis.

“It’s not enough to pull the excess that’s in the atmosphere at that time — we’d also have to pull out what went into the oceans,” he said. “If we want to undo this, we would have to artificially pull out all of the cumulative emissions since preindustrial times.”

Chelsea Harvey is a freelance journalist covering science. She specializes in environmental health and policy.